Typically degassing devices are classified according to the principles of the feed of the water to be degassed. In tray type deaerators water to be degassed flows along trays like a cascade, whether in a dome shaped section on top of the main vessel, whether in the main vessel itself or in a separate tank. In a spray type deaerator water to be degassed is sprayed into a vessel defining a deaeration chamber. The invention concerns a spray type deaerator.
The physical deaeration process occurring in a spray type deaerator comprises two stages: a pre-deaeration stage wherein water to be degassed is sprayed in the steam space (also known as pre-deaeration zone) of the deaeration chamber, usually the top area at one end of the vessel, and a final-deaeration in the main volume of the water contained in the deaeration chamber, where steam is brought in close contact with the water to be degassed. In the pre-deaeration zone the sprayer ensures heating of the water to saturation temperature and offers a large area for mass and heat transfer. The sprayed water is preheated by steam emerging from the main water volume contained in the vessel, into which steam is introduced, e.g. injected. At saturation conditions the solubility of the gases, e.g. oxygen, contained in the water is (almost) zero, resulting in a transfer of gases from the sprayed droplets to the surrounding steam atmosphere. Non-condensed gases and a small amount of steam are allowed to escape from the vessel. Final deaeration taking place in the main volume of water contained in the deaeration chamber is brought about by introducing steam or hot condensate. The treated water is discharged from the deaeration chamber, usually at the bottom of the vessel.
In a known spray type deaerator the top of the vessel is provided with a connecting pipe ending in a vessel flange for further connection to the source of water to be degassed. Typically this water has an overpressure compared to the pressure in the vessel. The flange is machined such that an annular carrying rim is provided adjacent the inner wall. A sprayer unit is suspended from a flange, which is bolted to the annular carrying rim of the flange, such that one or more spray nozzles of the sprayer unit are situated in the pre-deaeration zone of the deaeration chamber. The supply conduit of water is connected to the vessel flange via a counter flange. This vessel flange is not of a standard size due to its necessity of allowing the recessed rim to be machined. Therefore the vessel flange is manufactured on demand according to particular specifications. As a result this design of the vessel and sprayer involves high manufacturing costs.
From U.S. Pat. No. 2,689,018 A an apparatus for deaerating water is known, which comprises a tank having a water inlet pipe at its top, steam inlet pipe, water outlet pipe and drain line on its bottom and a vent for relatively non-condensable gases, principally air. In particular the apparatus has a neck, provided at the top of the tank, having a flange. A cover plate having a central aperture is bolted in registry with the opening in the water inlet pipe, which is bolted to the top of the cover plate. A cylindrical plate is formed integrally with a top plate, which is bolted to cover plate and to water inlet pipe. A depending tube is formed integrally with top plate in alignment with the opening in water inlet pipe. The top plate is provided with an aligned central opening allowing free communication between pipe and depending tube. A sprayer is mounted to this tube. This known construction is complex and is not easy to (dis)assemble for the purpose of servicing and maintenance.